1. Field of the Invention
The present invention relates to an apparatus for beautificating line drawings, which can effectively extract graphic data as input data to a CAD/CAM system or a geographic information management system from line drawing data.
2. Description of the Related Art
Along with recent developments in an information-oriented society, various "geographic information management systems" capable of managing complicated geographical systems such as waterworks, sewerage, and a power network in association with maps have been developed. Graphical input operations in a map database are time-consuming and expensive, as a matter of course. Various extensive studies have been made to automatically read graphic patterns illustrated in existing maps.
Since CAD/CAM systems have been very popular, a strong demand has also arisen for automatically reading graphic patterns or figures from existing design drawings. Many graphic pattern reading apparatuses have been developed to automatically extract graphic patterns such as a house from a map as a vector pattern or to read a line segment pattern from mechanical drawings.
Input data obtained by reading graphic information described in a map or mechanical drawing is adversely affected by noise components mixed in the read image data. During reading of information by an image scanner, the read graphic data are often distorted. A "modified-thinning" technique almost free from this distortion is employed in a conventional system to maintain beautification quality of graphic patterns upon removal of distortion of input read data. In particular, portions easily susceptible to distortion, such as an intersection, a corner, and a T-shaped portion constituted by line drawings, are manually beautificated. Although these conventional techniques are very effective as a means for compensating local distortions, they are not effective for global distortions. For example, a graphic pattern of a house read from a map is generally represented as a combination of orthogonal or parallel line segments. In practice, however, a graphic pattern of a house may be read and input as non-orthogonal or non-parallel line segments, or a circular graphic pattern may be read and input as an elliptical graphic pattern. Therefore, the "modified-thinning" technique cannot cope with the global distortions of graphic patterns.
As described above, in a conventional graphic pattern input apparatus (reading apparatus), although local distortions can be compensated by the "modified-thinning" technique, it is difficult to effectively correct global distortions. Therefore, several problems posed by a graphic data input apparatus for a geographic information management system, a CAD/CAM system, and the like are left unsolved.